The present invention relates to a motor-driven hand grinder, in particular an eccentric disk grinder.
Hand grinders of this type are known in the art. One of such hand grinders is disclosed for example in the European patent document EP 0 254 850 82. In this hand grinder the first rolling surface is formed as an outer toothed ring which rotates with the driven grinding disk around its axis, and a second rolling surface formed by an inner toothed ring on an outer tooth rim which is non rotatably held on the machine housing and is displaceable axially by an outer actuating device between an inoperative position and an operative position cooperating with the first rolling surface. In the inoperative position the second rolling surface is disengaged from the first rolling surface. In the operative position, to the contrary the second rolling surface can rotate substantially in the same geometrical plane as in the first rolling surface so that the first rolling surface during rotation of the grinding disk can roll on the second rolling surface, so that the eccentric movement of the grinding disk is superposed with a rotary movement around its eccentric axis. This leads to the situation that if the second rolling surface is located in the operational position, an increased workpiece wear occurs. Also, in the hand grinder there is the disadvantage that the conversion between the idle running and the positive drive is not possible during the operation of the hand grinder. During the axail relative displacement, damages can occur to the teeth of both rolling surfaces. It is also of disadvantage that the grinder has a relatively great structural height due to the arrangement of the rolling surfaces.
Accordingly, it is an object of present invention to provide a motor-driven hand grinder, in particular an eccentric disk grinder which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent hereinafter, one feature of present invention resides, briefly stated, in a motor-driven hand grinder, in which the second rolling surface is supported rotatably about its central axis, and a braking device is associated with the second associated surface, for interrupting or releasing a rotation of the second rolling surface around its central axis.
When the hand grinder is designed in accordance with the present invention, it has the advantage that a switching between free running and positive driving during the operation of the hand grinder can be performed without the danger of a damage and a reduced structural height with lower operational expenses is achieved.
In accordance with a preferable embodiment of the present invention, the actuating device of the braking device has a manually-operated eccentric lever which actuates the braking member and is provided with an eccentric cooperating with the braking member.
The eccentric lever can be supported turnably in the machine housing and can have a pin formed as an eccentric. It engages in an opening, for example in a loop, at the end of the braking member, in particular a braking band which embraces the outer peripheral surface of the outer toothed rim.
In a further advantageous embodiment of the invention, the eccentric lever has a handle located outside of the machine housing for turning actuation. Preferably the eccentric lever is designed so that a tensioning of the braking band is performed by turning around a peripheral angle of substantially 180xc2x0. The handle of the eccentric lever can be turned easily between two positions over of a peripheral angle of 180xc2x0, and thereby a conversion between the positive driving and the idle running can be performed during the operation of the hand grinder.
In accordance with a further embodiment of the present invention, the outer toothed ring is a part, in particular one-piece part, of the grinder disk unit, for example a one-piece component of the grinding plate on which the outer toothed ring is injection molded. This is especially simple and cost favorable and additionally contributes to the reduction of the structural heights.
In accordance with a further preferable embodiment, the inner toothed ring of the outer toothed rim has a greater number of teeth than the outer tooth ring. The tooth number difference can amount for example to two. It is thereby provided that with the adjustment the positive driving of the grinding plate is performed with a predetermined rotary speed. When for example the oscillation number amounts to 10,000, then the tooth number difference is two.
In accordance with a further preferable embodiment, the grinding disk unit has a sleeve which is coupled with the working spindle, in particular in a non-rotatable manner, and provided for example at its end side with an eccentric pin. The grinding disk unit also has a grinding disk which is held on the eccentric pin by a bearing and is connected with an eccentric pin, for example by a screw.
It is further advantageous when the outer toothed rim has a bearing ring located along the central axis at an axial distance from the inner toothed ring and is rotatably supported with the bearing ring by a bearing relative to the machine housing, in particular with respect to the sleeve which is coaxial to the axis of the working spindle. The bearing can be for example pressed on the sleeve, and the outer toothed ring can be pressed with its bearing ring on the outer ring of the bearing.
In accordance with a further advantageous embodiment, an impeller wheel of an inner dust aspiration is mounted on the sleeve. Alternatively, the impeller wheel can also sit directly non rotatably on the working spindle and can have a sleeve which is eccentric relative to the spindle axis. A cylindrical sleeve for end-side holding of the grinding disk can be rotatably supported in the sleeve by a bearing.
In accordance with a further preferable embodiment, the sleeve with the end-side eccentric pin can be formed as a sintered part and therefore produced in an especially cost-favorable manner. It can be advantageous when the outer toothed rim is formed of a light metal or zinc pressure cast, so as to also provide a cost-favorable design.
In a further advantageous embodiment of the invention, the grinding disk is formed with one-piece outer tooth ring which forms the first rolling surface and is composed of a one-piece synthetic plastic injection molded component. Thereby a further cost reduction and simplification is obtained.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.